The lumbar spine refers to the lower back, and is where a human spinal column curves inward toward the abdomen. The lumbar spine, which typically starts five to six inches below the shoulder blades, connects with the thoracic spine at the top and the sacral spine at the bottom. A human lumbar spine typically includes 5 vertebrae, although some individuals have 6 vertebrae in their lumbar spine. A typical single-level spinal segment includes a disk that is located between a cephalad vertebra and a caudal vertebra. The cephalad and caudal vertebrae are connected to each other primarily through the disk anteriorly and through a left and right facet joint posteriorly. The vertebrae are stabilized by ligaments, muscles, and their intrinsic facet geometry. The facet joints are bony projections from the posterior vertebrae that are capped with cartilage, and that articulate with each other. The disk and facet joints allow some mobility between the vertebral segments, while in tandem with the ligaments and muscles, also provide spinal stability. There are several different conditions that can cause pain in the lumbar and thoracic spine, including disk problems such as degenerative disk disease, facet degeneration, scoliosis and other deformities, trauma, tumor, infection, spondylolisthesis, stenosis, etc.
Non-operative treatments such as physical therapy, medications, and exercise may be appropriate for some of these conditions, but sometimes it is determined that surgery is necessary. A lumbar and/or thoracic spine fusion can be used to help alleviate pain and/or stabilize the spine in some individuals who are suffering from the aforementioned ailments. A spinal fusion may be performed in a variety of manners, including a conventional extensile open surgical approach through a midline posterior incision. Alternatively, a minimally invasive approach may be utilized, using a series of smaller incisions in order to minimize the physiological burden of surgery.
Spinal instrumentation systems, for example, pedicle screws and rods, are often used to stabilize the spine and improve the fusion rate, in both open and minimally invasive percutaneous procedures. Spinal instrumentation can be placed through a single extensile incision in conventional open surgery, or may be placed through a series of small incisions, which is commonly referred to as percutaneous pedicle screw instrumentation. The spinal instrumentation provides the stability component of the fusion operation, but a successful fusion also depends on a biological component, which is new bone growth between vertebral segments. In order for this new bone growth to occur and achieve fusion, the biological environment must favor bone growth. This biological component of the fusion typically depends on placement of bone graft or a bone growth promoting material between vertebral segments, which stimulates new bone growth from one vertebra to the next and results in a spinal fusion.